Abstrict

A filter cloth whose underside comprises substantially parallel,
additional yarns 8 that are thicker than the rest of the yarns of
the cloth, substantially parallel channels 9 being formed between
the yarns, wherein filtered liquid passed through the cloth is allowed
to flow in the direction of the surface of a filtering element 10
between the filtering portion of the cloth and the surface of the
element. The invention further relates to a filtering module manufactured
from the filter cloth of the invention.

Claims

What is claimed is:

1. A solid-liquid separation filter cloth composed of a plurality
of yarns in the transverse and the longitudinal directions, the
filter cloth comprising a filtering portion having a structure and
density according to desired filtering characteristics for separating
liquid from a mixture consisting of solids and liquid, whereby the
liquid in the mixture passes through the filter cloth and the solids
in the mixture remains on a surface of the filter cloth, and which
filter cloth is further to be arranged against a filtering element
in a filtering apparatus, and an underside of the filter cloth,
i.e., a portion facing the filtering element, comprises substantially
parallel yarns that are thicker than the rest of the yarns of the
cloth, and that the thicker yarns are placed at predetermined intervals
defined by the other yarns of the filter cloth extending parallel
thereto to provide desired parallel channels therebetween to enable
the filtered liquid to flow in the direction of the surface of the
filtering element between the filtering portion of the filter cloth
and the filtering element.

2. The solid-liquid separation filter cloth as claimed in claim
1, wherein the thicker yarns are monofilaments, and that at least
the yarns of the filter cloth that are parallel with the thicker
yarns in the bottom and located at the thicker yarns are multifilaments,
whereby the multifilament yarns have been moulded at the thicker
yarns and thus form dense cloth also at the thicker yarns.

3. The solid-liquid separation filter cloth as claimed in claim
1, wherein the diameter difference between the other yarns and the
thicker yarns of the filter cloth is at least 1:1.4 or more.

4. The solid-liquid separation filter cloth as claimed in claim
1, wherein the thicker yarns in the underside of the filter cloth
have the same direction as a weft.

5. The solid-liquid separation filter cloth as claimed in claim
1, wherein at least some of the yarns used in the filter cloth are
heat-shrinkable.

6. The solid-liquid separation filter cloth as claimed in claim
1, wherein batt has been needled to the filtering portion of an
upper surface of the filter cloth, i.e., a surface facing away from
the filtering element, to obtain a denser structure.

7. A solid-liquid separation filtering module to be arranged on
a filtering element as a filtering surface when liquid is separated
from a mixture consisting of solids and liquid by means of a filtering
apparatus, which filtering module is made of filter cloth comprising
a filtering layer composed of yarns in the transverse and the longitudinal
directions whereby the liquid in the mixture passes through the
filter cloth and the solids in the mixture remains on a surface
of the filter cloth, and an underside of the filter cloth, i.e.,
the surface to be against the filtering element, is comprised of
substantially parallel yarns that are thicker than the other yarns
of the filter cloth, and that desired channels are provided between
the thicker yarns by the placement of the thicker yarns at predetermined
intervals defined by the other yarns of the filter cloth extending
parallel thereto, wherein the liquid filtered by the cloth is allowed
to flow in the direction of a surface of the filtering element.

8. The solid-liquid separation filtering module as claimed in claim
7, wherein, the filter cloth is arranged such that the channels
in the bottom of the cloth are directed according to a structure
of the filtering module.

9. The solid-liquid separation filtering module as claimed in claim
7, wherein the filter cloth is arranged such that the channels in
the bottom of the cloth are directed such that the channels lead
the filtered liquid to openings in the filtering element.

10. The solid-liquid separation filtering module as claimed in
claim 7, wherein the filtering module comprises heat-shrinkable
yarns, allowing the filtering module to be stretched over the filtering
element by thermal treatment.

11. A solid-liquid separation filtering apparatus, comprising:
a filtering module; and a filtering element, wherein the filtering
module is arranged on a filtering element as a filtering surface
where liquid is separated from a mixture consisting of solids and
liquid where, the filtering module is made of a filter cloth comprising
a filtering layer composed of yarns in the transverse and the longitudinal
directions whereby the liquid in the mixture passes through the
filter cloth and the solids in the mixture remains on a surface
of the filter cloth, and an underside of the filter cloth, i.e.
the surface to be against the filtering element, comprises of substantially
parallel yarns that are thicker than the other yarns of the filter
cloth, and desired channels are provided between the thicker yarns
by the placement of the thicker yarns at predetermined intervals
defined by the other yarns of the filter cloth extending parallel
thereto, wherein the liquid filtered by the filter cloth is allowed
to flow in the direction of a surface of the filtering element.

12. The solid-liquid separation filtering apparatus as claimed
in claim 11, wherein the filtering module is arranged such that
the channels in the bottom of the cloth are directed according to
a structure of the filtering module.

13. The solid-liquid separation filtering apparatus as claimed
in claim 11, wherein the filtering module is arranged such that
the channels in the bottom of the cloth are directed such that the
channels lead the filtered liquid to openings in the filtering element.

14. The solid-liquid separation filtering apparatus as claimed
in claim 11, wherein the filtering module comprises heat-shrinkable
yarns, allowing the filtering module to be stretched over the filtering
element by thermal treatment.

Description

[0001] This is a Division of application Ser. No. 09/986,422 filed
Nov. 8, 2001, which in turn is a Continuation of International Application
PCT/F100/00413 filed May 9, 2000 which designated the U.S. and was
published under PCT Article 21(2) in English. The entire disclosure
of the prior applications is hereby incorporated by reference herein
in its entirety.

FIELD OF THE INVENTION

[0002] The invention relates to filter cloth composed of a plurality
of yarns in the transverse and the longitudinal directions, the
filter cloth comprising a filtering portion having a structure and
density according to desired filtering characteristics for separating
liquid from a mixture consisting of solids and liquid, and which
filter cloth is further to be arranged against a filtering element
in a filtering apparatus, and the structure of the underside of
the filter cloth, i.e. a portion facing the filtering element, comprises
thicker yarns than a portion facing the upper side of the cloth
for the flow of liquid filtered by the cloth.

[0003] The invention further relates to a filtering module to be
arranged on a filtering element as a filtering surface when liquid
is separated from a mixture consisting of solids and liquid by means
of a filtering apparatus, which filtering module is made of filter
cloth comprising a filtering layer composed of yarns in the transverse
and the longitudinal directions, thicker yarns than the rest of
the yarns of the cloth having been arranged while manufacturing
the cloth in the bottom of the filter cloth for the flow of liquid.

BACKGROUND OF THE INVENTION

[0004] Different machine screens, such as disc filters and drum
filters, are used for removing liquid from a mixture consisting
of liquid and dry solids. A disc filter typically comprises a plurality
of triangular filter segments arranged in a rotating frame onto
which segments are arranged filter bags made of filter cloth. The
liquid in the mixture to be filtered is allowed to penetrate through
the filter cloth and further into a segment through openings extending
to the surface of the filter segment. In addition to the segments,
depending on the structure of the filter, different box-like and
cylinder-like pieces and other elements are used onto which a bag
or a similar filtering module made of filter cloth is stretched
by means of different mechanical tightening parts or, nowadays increasingly
often, by thermal contraction. It has been found out that if compact
filter cloth is in use allowed to be pressed tightly against the
surface of the filtering element, the flow of the passed liquid
is hindered between the filtering cloth and the element to the openings
of the element. In order to prevent this problem, a separate "additional
wire bag" has been introduced between the actual filtering
bag and the filtering element. The backing wire bag is made of a
netlike texture forming a loose, highly permeable layer in the transverse
direction of the surface of the cloth between the compact filtering
bag and the surface of the element. Although such a separate backing
wire bag does work relatively well in practice, fitting the backing
wire bag is, however, an additional stage of operation. Furthermore,
the manufacturing also causes additional costs.

[0005] SE 431 826 discloses filter cloth for separating solid particles
and liquid, comprising at least two interwoven layers: a filtering
layer and a supporting layer. In the supporting layer, i.e. in the
portion facing the filtering element, thicker yarns are to be used
in order to achieve a more coarse bottom. A drawback of the disclosed
solution is, however, that the liquid that has already passed the
filtering layer in the direction of the surface of the filtering
element flows inside the supporting texture of the filter cloth.
As normally, the texture comprises yarns travelling crosswise and
having different directions, whereby the yarns form obstacles to
an efficient flow of liquid.

SUMMARY OF THE INVENTION

[0006] An object of the present invention is to provide filter
cloth and a filtering module manufactured from the same which avoid
drawbacks of the known solutions.

[0007] The filter cloth of the invention is characterized in that
the underside of the filter cloth comprises substantially parallel
yarns that are thicker than the rest of the yarns of the cloth,
and that the thicker yarns form parallel channels therebetween in
order to enable the filtered liquid to flow in the direction of
the surface of the filtering element between the filtering portion
of the filter cloth and the filtering element.

[0008] The filtering module of the invention is further characterized
in that the filtering module is manufactured from filter cloth whose
underside, i.e. the surface to be against the filtering element,
comprises substantially parallel yarns that are thicker than the
rest of the yarns of the cloth, and that channels are formed between
the thicker yarns, in which channels the liquid filtered by the
cloth is allowed to flow in the direction of the surface of the
filtering element.

[0009] The idea underlying the invention is that the filter cloth
is produced such that while weaving the cloth, parallel, thicker
yarns are arranged on the underside of the cloth, i.e. the surface
facing the filtering element, the yarns forming therebetween parallel
channels on the underside of the cloth to enable the filtered liquid
to flow in the direction of the surface of the filtering element.
The parallel, thicker yarns are additional yarns in regard to the
rest of the structure of the filter cloth; hence, they are irrelevant
to the rest of the structure of the cloth. Furthermore, the yarns
used in the cloth that travel at the thicker yarns and have the
same direction as the thicker yarns are preferably multifilaments,
whereby they set tightly in the cloth in the vicinity of the monofilament,
thicker yarns. Hence, the thicker yarns do not impair the density
of the cloth. Furthermore, the filter cloth can be directed in the
filtering module such that the flow channels on the underside of
the cloth are located according to the positions of the openings,
i.e. the channels direct the liquid to the openings. Owing to the
thick yarns, the dense, filtering texture portion of the filtering
module is located at a distance from the surface of the filtering
element.

[0010] An advantage of the invention is that by manufacturing filter
bags to be fitted onto different filtering elements and similar
replaceable filtering modules from the filter cloth of the invention,
the use of separate backing wire bags is avoided. Hence, it is easier
and quicker to change the filter bags, and no further costs result
from an additional bag. Furthermore, even thin filter cloth can
be made stiff thanks to the thick yarns in the bottom of the cloth.
A stiff filtering module stays better in place and thus lasts longer
in use. Furthermore, the thick yarns in the bottom protect the actual
filtering layer of the cloth, whereby sharp edges or the like of
the filtering element cannot damage the cloth. In regard to the
SE publication mentioned in the description of the prior art, the
filter cloth of the invention can be more readily cleaned during
use since dirt does not become clogged up in the open channels in
the bottom of the cloth of the invention in such a manner as dirt
can be clogged in different texture structures. A substantial advantage
is that now the filtered liquid does not flow inside the texture
structure but in the flow channels formed for the purpose, wherein
there are no yarns in the transverse direction of the channels to
block the flow. Furthermore, the flow of liquid can be directed
in a desired manner when the filtering module is manufactured such
that the parallel flow channels in the bottom of the filter cloth
are arranged according to the positions of the openings and the
operation of the filtering element. It is then possible to arrange
the openings of the filtering element and the channels of the filter
cloth in such a manner that liquid is allowed to enter the openings
of the filtering element and further on as efficiently as possible.
All in all, by using the filter cloth of the invention, the working
costs of the filtering apparatus can be reduced and the filtering
efficiency improved.

BRIEF DESCRIPTION OF THE FIGURES

[0011] The invention will be described in closer detail in the
following drawings, in which

[0012] FIG. 1 schematically shows the principle of a filtering
apparatus wherein a filtering module manufactured from filter cloth
of the invention can preferably be used,

[0013] FIG. 2 schematically shows a structure of filter cloth of
the invention, and

[0014] FIG. 3 schematically shows a filtering module made of filter
cloth of the invention, fitted onto a filtering element.

DETAILED DESCRIPTION OF THE INVENTION

[0015] FIG. 1 is a simplified view of the principle of a disc filter
2 comprising a plurality of filtering segments 1a to 1h. The disc
of the filter rotates in a basin (not shown) containing liquid and
solids, whereby the liquid in the mixture passes through the filter
cloth stretched over the segments. The solids then remain on the
outer surface of the filter cloth, wherefrom the solids are removed
by means of doctor blades, water jets or some such washing apparatus.
The liquid that has passed the filter cloth flows to openings 3
provided in a filtering segment and therethrough further into the
filtering element, from which it is directed forward via a duct
4. For the sake of clarity, the openings 3 are depicted highly enlarged
in the figure. For the same reason, the other segments 1b to 1h
are indicated in dotted lines and totally without openings. As can
be seen from the figure, the openings have the same direction as
the central axle of the segment but, of course, the openings can
be arranged into lines having a different direction, or, alternatively,
the entire filtering surfaces of the segment may be evenly provided
with openings. When the openings are located according to the figure
and the filtering module is formed according to the line formed
by the openings, the flow channels formed by the thick yarns on
the underside of the module have the same direction as the openings.
For illustrative reasons, the direction of the thick yarns in the
bottom of the module has been indicated in dotted lines 5 in the
figure. When the openings and the flow channels are formed in this
manner, the liquid that has passed through the cloth flows efficiently
to the openings and further into the segment because of the rotation
of the filtering apparatus and gravity.

[0016] In a highly simplified manner, FIG. 2 shows a cross-sectional
structure of filter cloth of the invention. The filter cloth according
to the figure is single-layer filter cloth comprising warp yarns
6 and weft yarns 7. Furthermore, thicker yarns 8 having the direction
of the weft have been woven on the surface of the bottom of the
cloth. The thicker yarns are additional yarns, i.e. each thicker
yarn has been arranged parallel to and against a weft yarn 7a located
at the thicker yarn. The parallel, thicker yarns form flow channels
9 therebetween, whereby the liquid filtered by the cloth is allowed
to flow via the channels and directed by the channels to the openings
3 provided in a filter element 10. The thicker yarns are monofilaments
that are highly tolerant of compression. The warp and weft yarns,
in turn, are multifilaments because they allow easier formation
of a dense texture. Furthermore, in the cloth of the invention,
they flatten out and become appropriately moulded at the thicker
yarns, whereby the cloth becomes compact regardless of the thicker
yarns in the bottom. This can be seen in FIG. 2 by examining particularly
the weft yarns 7a located at the thicker yarns 8. Also spun yarn
can be used in the filtering portion. Further, the structure may
comprise other monofilament yarns than the thick yarns in the bottom.
A monofilament having the same direction as the thick yarns and
improving the stiffness of the cloth has been indicated in the figure
by reference number 11. However, the parallel yarns adjacent to
the thick yarns are, due to the compactness, preferably multifilaments
or spun yarns. Thanks to the thicker yarns, the cloth is stiff even
if the actual filtering layer were extremely thin. Thanks to a stiffer
structure, the filtering module stays better in place regardless
of the filtering and cleaning forces that it is subjected to, and,
consequently, lasts longer. On the other hand, a thin filtering
layer does not become clogged as easily as a thick layer, and it
can be washed more readily. Furthermore, the thick yarns in the
bottom protect the actual filtering layer e.g. in the corners of
the filtering element wherein the filter cloth is subjected to high
stress while being stretched.

[0017] FIG. 2 also shows that the thicker yarns 8 can be arranged
at desired intervals in the cloth. The number of the thicker yarns
in relation to the other parallel yarns in the bottom can be determined
according to the use and the desired characteristics, e.g. stiffness,
required of the cloth.

[0018] The filtering module can be stretched over the filtering
element by means of different mechanical stretching parts known
per se or the stretching can be carried out by thermal contraction,
in which case at least some of the yarns of the filter cloth must
be heat-shrinkable. In this connection, heat-shrinkable yarn refers
to yarn used in manufacturing filter cloth that can be shortened
by heating to such an extent that the resulting change in length
can be utilized in a desired manner in order to stretch filter bags,
filter wires or the like tightly in place. The stretching can be
controlled by selecting the yarns appropriately. Since the thicker
yarns only contract substantially in their longitudinal direction
and not in relation to their diameter, the channels, while being
contracted, substantially retain their shape; consequently, the
contraction does not impair the flow of liquid. On the other hand,
the thicker yarns do not have to be shrinkable; it is usually enough
that the transverse yarns in relation to the thicker yarns are shrinkable.
Also in such a case, the channels retain their structure regardless
of the contraction.

[0019] FIG. 3 is a sectional view of a part of a filtering module
that has been fitted in place. In this case, the filtering element
10 is a cylinder, openings 3 having been provided through the surface
of the cylinder. The thicker yarns 8 in the bottom of the cloth
form channels 9 at the openings in the manner shown in the figure.
For the sake of clarity, the two-layer filter cloth is shown in
a highly simplified manner in the figure. It is believed in this
connection that a person skilled in the art can select an appropriate
bonding type, yarn material, yarn type, etc. The filter cloth can
thus be a single- or multilayer texture and it can be made of yarns
having a different cross section, as long as the yarn material is
durable and has dimensional stability under the planned working
conditions. Thick yarns per se do not affect the characteristics
of the filtering layer, so in that sense they are additional yarns
in the cloth. The diameter difference between the other yarns and
the thicker yarns is preferably between 1:1.4 to 1:6, whereby a
sufficiently large channel can be provided between the filtering
layer of the cloth and the surface of the element as far as the
flow of liquid is concerned. A person skilled in the art can determine
the difference in thickness between the multi- and monofilaments
by calculating, for example.

[0020] The drawing and the related description are only intended
to illustrate the idea of the invention. In its details, the invention
may vary within the scope of the claims. Hence, the actual filtering
layer of the filter cloth can be formed by needling thickening batt
into the body texture. The thickening effect can also be achieved
by an appropriate coating layer to be arranged on the upper surface
of the cloth. In principle, at least, it is also possible to use
a body formed from non-woven yarn arrangements. Further, elements
known as shrink wires to be arranged on different drum filters and
the like can also be manufactured from the filter cloth of the invention.
Furthermore, by directing the filter cloth appropriately, desired
points of the module can be made stiff by means of the thick yarns
in the bottom. Bent transversely to the thick yarns, the cloth is
stiff, but when the cloth is bent in the direction of the thick
yarns, it bends readily over a section between the thick yarns.
In addition, the cloth can be manufactured such that the thicker
yarns in the surface structure of the bottom of the cloth have,
as distinct from what has been disclosed above, the same direction
as the warp.